A read channel integrated circuit (IC) is one of the core electronic components in a modern hard disk drive. In a magnetic recording system, for example, a read channel converts and encodes data to enable magnetic recording heads to write data to a magnetic medium and to then read back the data accurately. The magnetic media in a magnetic recording system have a number of tracks and each track comprises “read” sectors, with “servo” sectors embedded between the read sectors. The information recorded in the servo sectors helps to position a magnetic recording head so that the user information stored in the read sectors can be retrieved properly.
The servo and read sectors both typically begin with the same known preamble pattern. The read preamble is followed by a read address mark and encoded user data. The servo preamble is followed by a servo address mark and various servo data, including encoded Gray data (often referred to as servo data).
U.S. patent application Ser. No. 13/281,923, filed Oct. 26, 2011, entitled “Methods and Apparatus for Validating Detection of RRO Address Marks,” incorporated by reference herein, describes an exemplary magnetic recording system that encodes the servo sector using asynchronous Wide Bi Phase (WBP) encoding. Thus, a binary zero is encoded as “1100” and a binary one is encoded as “0011” to provide a large positive sample or a negative sample at the wide bi-phase code word boundary. The sample can be sliced with a threshold of zero to detect the servo data bits. When the samples are large, the servo data bits are properly detected. Due to noise, however, the amplitude of the samples may be lowered closer to zero, causing detection errors.
A need therefore exists for improved techniques for detecting servo sector data in a magnetic recording system.